1. Field of the Invention
The present invention relates to digital resistive-type touch panels. More particularly, the present invention relates to a digital resistive-type touch panel having an increased ratio of viewing area to dead space.
2. Discussion of the Related Art
Information devices such as personal computers, mobile transmission devices, etc., use a variety of input devices such as keyboards, mice, digitizers, etc., to effect textual and other graphic processes. As the demand for information devices that are mobile and simple to use continues to increase, research into replacing relatively large input devices such as keyboards and mice has been performed to develop input devices that are easier to carry, and simpler to operate, than conventional input devices. In particular, much research has been directed to allowing information to be input via portable input devices using contact objects such as a user's finger. Recently, durable and reliable input devices have been developed that not only to satisfy general input functions, but have entirely new types of functions.
Touch panels have been developed as a means of efficiently interfacing with electronic devices via a display surface. Depending on the type of contact object used (e.g., a user's finger, a stylus, etc.), and depending on the manner in which the location of a contact point (i.e., the location where the contact object is operably proximate the touch panel) is determined, touch panels are generally classifiable as resistive-type, capacitive-type, electromagnetic (EM)-type, saw-type, and infrared-type touch panels.
Owing to their thin profile, small dimensions, and low power consumption characteristics, resistive-type touch panels are commonly integrated with liquid crystal display (LCD) devices is in applications such as electronic notebooks, personal digital assistants (PDAs), mobile PCs.
Generally, analog resistive-type touch panels include two resistive sheets (i.e., substrates) oppositely arranged and spaced apart from each other by a predetermined distance using a plurality of dot spacers. More specifically, the resistive sheets are generally formed of film-type substrates between 0.11 mm and 0.2 mm thick, glass substrates between 0.2 mm and 2 mm thick, or plastic-type substrates between 1 mm and 2 mm thick. When a contact object (e.g., a user's finger, a stylus pen, etc.) contacts a predetermined portion of an upper substrate arranged over a display surface (i.e., when a user generates a contact point), an electrode formed on the upper substrate electrically contacts an electrode formed on a lower substrate. Subsequently, a variable voltage value, corresponding to the location of the contact point, is transmitted to a control unit that calculates the coordinates of the contact point.
Contrary to analog resistive-type touch panels, digital resistive-type touch panels include a plurality of patterned transparent electrodes formed on both the upper and lower substrates so as to create a matrix pattern of transparent electrodes. When a contact object generates a contact point, predetermined ones of the patterned transparent electrodes of the upper and lower films electrically contact each other at the contact point. Subsequently, a voltage value corresponding the location of the contact point is transmitted from the upper and lower substrates to a control unit that calculates the coordinates of the contact point.
FIG. 1 schematically illustrates a related art digital resistive-type touch panel. FIG. 2 illustrates a cross-sectional view taken along line A-A′ of FIG. 1.
Referring to FIG. 1, the related art digital resistive-type touch panel includes a viewing area V/A 10 having dimensions (e.g., rectangular dimensions) corresponding to a viewable display surface of an LCD device (not shown), and a dead space region 15, formed to surround the periphery of the viewing area V/A 10 and having dimensions corresponding to a non-viewable region of the LCD device.
Referring to FIG. 2, a lower substrate 1 is bonded to an upper substrate 2 via an insulating adhesive material 21 and 22 arranged in the dead space region 15. Dot spacers (not shown) are arranged between the bonded lower and upper substrates 1 and 2. A first plurality of patterned transparent electrodes 40 extend along a first direction on a lower surface of the upper substrate 2 and a second plurality of patterned transparent electrodes 30 extend along a second direction on an upper surface of the lower substrate 1, wherein the second direction is generally perpendicular to the first direction.
During operation of the digital resistive-type touch panel, a unique voltage is applied from a signal line 7 to each of the first plurality of patterned transparent electrodes 40 such that, when a predetermined portion of the upper substrate 2 is contacted with a contact object (e.g., a user's finger, a pen, etc.), one of the first plurality of patterned transparent electrodes 40 electrically contacts one of the second plurality of patterned transparent electrodes 30 at a location corresponding to the contact point generated by the contact object. Accordingly, a unique voltage value is transmitted by the lower substrate 1 to the signal line 7, wherein the transmitted voltage value corresponds to X and Y coordinates of the generated contact point. As is evident from the discussion above, if a contact point is generated by a contact object in a region of the touch panel where the first and second plurality of patterned transparent electrodes 30 and 40 are not formed, it is impossible to determine the coordinates of the contact point.
FIGS. 3A and 3B illustrate plan views of the related art digital resistive-type touch panel lower and upper substrates and the plurality of patterned transparent electrodes formed thereon.
Referring to FIG. 3A, the first plurality of patterned transparent electrodes 40 are formed within the viewing area 10 of the upper substrate 2. Moreover, the first plurality of patterned transparent electrodes 40 are spaced apart from each other by a predetermined distance and extend over the surface of the upper substrate 2 along a first direction (e.g., an X-axis direction). A first plurality of signal lines 7a are arranged within the dead space region 15 for transmitting unique voltages to respective ones of the first plurality of patterned transparent electrodes 40.
Referring to FIG. 3B, the second plurality of patterned transparent electrodes 30 are formed within the viewing area 10 of the lower substrate 1. Moreover, the second plurality of patterned transparent electrodes 30 are spaced apart from each other by a predetermined distance and extend over the surface of the lower substrate 1 along a second direction perpendicular to the first direction (e.g., a Y-axis direction). A second plurality of signal lines 7b are arranged within the dead space region 15 for transmitting a voltage applied from one of the first plurality of patterned transparent electrodes 40 and transmitted by a respective one of the second plurality of patterned transparent electrodes 30.
Generally, the first and second plurality of patterned transparent electrodes 30 and 40 are formed by selectively patterning a transparent conductive layer such as Indium-Tin-Oxide (ITO) while the first and second plurality of signal lines 7a and 7b are formed of a low sheet resistance material such as silver (Ag). The first and second plurality of signal lines 7a and 7b are connected between their respective patterned transparent electrodes 30 and 40 and a Flexible Printed Cable (FPC) film (not shown) provided at one side of the touch panel.
Moreover, the upper substrate 2 is formed of flexible plastic film such as Polyethylene Terephtalate (PET) while the lower substrate 1 is formed of a flexible PET film, or a thin glass substrate. By forming the lower substrate 1 out of the thin glass substrate, isotropic optical properties are realized. Accordingly, the reflectivity of the lower substrate 1 can be decreased by forming a polarizing plate (not shown) on the thin glass substrate. Recently, however, plastic films having isotropic optical properties have been developed and used as materials from which the lower substrate 1 can be formed.
Use of the aforementioned related art digital resistive-type touch panel is disadvantageous, however, because, the first and second plurality of signal lines 7a and 7b must apply voltage signals to respective ones of the patterned transparent electrodes 30 and 40, wherein the plurality of signal lines 7a and 7b are connected to an FPC film arranged at one side of the touch panel. As a result, an excessively large dead space region 15 is required to accommodate the first and second plurality of signal lines and the size of the viewing area 10 is undesirably reduced. Moreover, when the plurality of signal lines are arranged along one direction as shown in FIGS. 3A and 3B, the signal lines connected to the patterned transparent electrode arranged farthest from the FPC become relatively longer than other ones of the signal lines, thereby distorting signals they transmit